1. Field of the Invention
The present invention relates to a data processing method, a data processing apparatus, a mask generating method, and a mask pattern, and more specifically, to mask processing or a mask pattern for generating dot print data for dividedly forming ink dots constituting a print image by means of plural scans of a print head.
2. Description of the Related Art
Ink jet printers widely employ what is called a multi-path printing system. The multi-path printing system is a system that dividedly forms ink dots constituting an arbitrary area in an image by means of plural scans of a print head. This system can distribute an uneven density, which results from a variation in ejecting performance such as the direction in which ink is ejected from each nozzle (or ejection opening) or an error in conveyance of a print sheet, into plural scans. This enables high grade images with unnoticeable density unevenness to be printed.
A mask process using a mask pattern (also simply referred to as a “mask”) is generally executed for generating dot print data required to dividedly form plural ink dots constituting a print image by means of plural scans. The mask pattern is what arranges pixels that permit printing (hereinafter also referred to as “print permitting pixel”) and pixels that do not permit printing (hereinafter also referred to as “print non-permitting pixel”) as described below in FIG. 5. The print permitting pixels correspond to black parts in FIG. 5, whereas the print non-permitting pixels correspond to white parts in FIG. 5. The mask patterns may have forms according to various purposes such as adjusting the number of print dots for each of the plural scans and reducing the density unevenness, by creating the arrangement of the print permitting pixels in the mask pattern;
For example, the two types of mask patterns described below are effective on an image quality.
A typical mask pattern is known as a mask pattern based on a Beyer type pattern. However, such mask pattern has regular arrangement of the print permitting pixel and is likely to cause interference with image data. This may disadvantageously degrade image quality.
Thus, Patent Document 2 discloses using the mask pattern in which the print permitting pixels are randomly arranged (hereinafter referred to as a random mask) to prevent interference of the mask with image data from occurring. This serves to solve the above problem.
On the other hand, Patent Document 1 describes that a mask pattern is generated so that arrangement of the print permitting pixels has high dispersiveness and such a highly dispersive mask pattern is used to suppress degradation of images resulting from the deviation of dot formation positions during bidirectional printing. More specifically, the arrangement of the print permitting pixels in the mask described in Patent Document 1 is appropriately dispersed using the concept of a repulsive potential. In other words, this mask pattern is generated so as to avoid arranging dots formed by using this mask pattern close to one another, as mush as possible. Thus, in terms of frequency components, the arrangement of the print permitting pixels has few low-frequency components. With this mask, even if positions of dots formed by bidirectional printing deviate from each other and thereby textures of the mask pattern itself appear significantly in the print image, the textures are difficult to be visible because of their appropriate dispersion.    Patent Document 1: Japanese Patent Application Laid-Open No. 2002-144552    Patent Document 2: Japanese Patent Application Laid-Open No. 7-052390    Patent Document 3: Japanese Patent Laid-Open Application No. 2002-96455